<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      .arrow {
        display: inline-block;
        margin-right: 10px;
        /* 基础样式 */
        width: 0;
        height: 0;
        /* 基础样式 */
        border: 16px solid;
        border-color: transparent #cddc39 transparent transparent;
        position: relative;
      }

      .arrow::after {
        content: "";
        position: absolute;
        /* 通过位移覆盖背景 */
        right: -20px;
        top: -16px;
        border: 16px solid;
        border-color: transparent #fff transparent transparent;
      }
      /*下*/
      .arrow.bottom {
        transform: rotate(270deg);
      }
      /*上*/
      .arrow.top {
        transform: rotate(90deg);
      }
      /*左*/
      .arrow.left {
        transform: rotate(180deg);
      }
      /*右*/
      .arrow.right {
        transform: rotate(0deg);
      }
    </style>
  </head>
  <body>
    <div class="box">
      <div class="box-inner">
        <div class="arrow bottom"></div>
        <div class="arrow top"></div>
        <div class="arrow right"></div>
        <div class="arrow left"></div>
      </div>
    </div>
  </body>
</html>
